Echinococcus granulosus: absorption of cycloleucine and α-aminoisobutyric acid by protoscoleces

Abstract

Protoscoleces of Echinococcus granulosus absorb the amino acids cycloleucine and alpha-aminoisobutyric acid (AIB) by a combination of mediated uptake and diffusion. After correcting for the latter, values for Kt and Vmax of 0.124 mM and 0.947 nmoles/mg protein/2 min for cycloleucine were calculated; corresponding values for AIB were 0.039 mM and 0.139 nmoles/mg protein/2 min. Both amino acids were accumulated against a concentration gradient and a comparison of Kt and Ki values determined in mutual inhibition experiments suggested that both cycloleucine and AIB share a common uptake locus (loci). Cycloleucine uptake was pH-dependent and could be inhibited by a variety of other amino acids. Neither D- nor L-proline inhibited cycloleucine absorption but D-methionine, D-alanine, D-leucine, D-valine and D-serine were much more effective inhibitors than their L-counterparts.

Ontogenetic changes in helminth membrane function

“…The uptake data derived from protoscoleces in these studies may thus reflect a combination of the permeability properties of both the evaginated scolex -neck of the presumptive adult worm and the soma of the protoscolex. Jeffs & Arme (1986) demonstrated the existence of membrane receptors for the transport of amino acids on protoscoleces. Active transport of cycloleucine and a-aminoisobutyrate (AIB) was shown and data suggested that both these amino acids shared a common uptake system.…”

Echinococcus granulosus: specificity of amino acid transport systems in protoscoleces

“…All materials and methods are as previously described by Jeffs & Arme (1986). Except where indicated, mean uptake is denoted by v, in units of nmoles/mg protein/2 min.…”

“…Table 1. Concentration ratios and post-absorptive metabolism {for details see text) Jeffs & Arme (1986). f AIB, a-aminoisobutyric acid.…”

“…This paper reports the findings of a study involving the uptake of L-proline and a further 7 L-amino acids by protoscoleces. These data, together with those obtained for cycloleucine by Jeffs & Arme (1986), have enabled the number and specificities of the transport loci by which these compounds enter the protoscolex to be determined, and permit an evaluation of their potential in drug-targeting.…”

“…Because of this we are studying the transport of a variety of low molecular weight organic nutrients and macromolecules, not only in an attempt to improve our knowledge of hydatid nutritional mechanisms but also in the hope that parasite-specific transport systems may be revealed which could lend themselves to more rational approaches to chemotherapy, such as drug-targeting. In a recent publication (Jeffs & Arme, 1986), it was established that the uptake characteristics of 1-aminocyclopentane-l-carboxylic acid (cycloleucine) by the protoscolex of Echinococcus granulosus were unusual in two respects. First, that certain D-amino acids were far more effective inhibitors of cycloleucine than the L-isomers, indicating their greater affinity for the cycloleucine transport systems, and second, that L-proline did not significantly inhibit cycloleucine uptake, suggesting the presence of a specific L-proline transport system(s).…”